The edger system of a plate mill for rolling plate steel generally includes rougher rolls which rotate about a pair of vertically spaced horizontal axes, coupled with a pair of edger rolls that rotate about a pair of horizontally spaced vertical axes. The rougher rolls reduce the thickness of the steel plates while the edger rolls work on the edges of the plate to keep them square and/or control plate width. Obviously both the rougher rolls and the edger rolls are adapted to move closer together or further apart, depending on the thickness and width of the plate being rolled and all of these rolls must be driven in order to feed the plate therethrough.
The drive to the vertical edger rolls usually will include a main drive shaft, extending across the machine, i.e. substantially horizontally, which is geared to two pinion shafts that extend vertically, there being one pinion shaft for each edger roll. A pinion is mounted to rotate with each pinion shaft and each such pinion is adapted to cooperate with the bull gear that in turn is coupled to drive one of the edger rolls.
The manner in which the bull gear is coupled to its respective edger roll depends on the type of drive mechanism employed which in turn is dependent on the manner in which the relative position of the two edger rolls is adjusted. In some cases the bull gear shaft is connected to the edger roll and the positions of the edger rolls are adjusted by rotating the bull gears about the axes of the pinion shafts thereby to move the two edger rolls toward and away from each other.
In another type of drive the bull gear is hollow and is fixed. A shaft passes up through and is coupled to the top end of the bull gear via a universal joint. The opposite end of the drive shaft is coupled to an edger roll by means of a second universal joint. The clearance between the shaft and the inside of the bull gear provides clearance to permit movement of the drive shaft when the adjusting mechanism of the edge rolls shifts the position of the edge rolls (in this type of mechanism generally upper and lower ends of the edger rolls are received within the bearings and the positions of these bearings are adjustable by some jacking means such as screw jacks and the like).
In each of the above drive systems one of the key elements is the pinion shaft with its pinion and driving gear, the driving gear usually being a bevel gear cooperating with a bevelled gear on the transversed main drive shaft of the machine. The diameter of the bevel gear is larger than the diameter of the pinion and thus vertical movement of the pinion shaft with the bevel gear attached result in the bevelled gear moving toward the underside of the bull gear and this poses limitations in the manner in which the housing mounting of the pinion shaft has been constructed to permit withdrawl of the pinion shaft.
One design requires that the whole upper drive unit, i.e. the pinion, bull gear, bevel gear, pinion shaft and the upper housing including the top of the main casing be lifted as a unit so that the whole mechanism may be lifted vertically. The upper housing is unbolted from the bottom casing, the bull gears disconnected from the edger rolls and then the whole unit, including the upper housing top plate of the main casing bull gears, etc. is lifted vertically until the bevel gears clear the bottom casing and then transported to the desired location. This assembly is quite heavy and could be in the order of 500,000 pounds, and a very large (high lifting capacity) crane is required to move the assembly.
In an alternative arrangement the upper housing is made relatively large and both the upper thrust bearing and the intermediate bearing are contained in their respective capsules which are rigidly interconnected. The upper capsule containing the thrust bearing is securely fixed to the top of the upper housing. To dismantle or assemble such a structure it is necessary to free the upper capsule and then lift the assembly formed by the pinion shaft and its connected gears as well as the upper and lower capsules vertically to clear the capsules from the apertures in the housing. These capsules are each slightly larger in diameter than the bevelled gear and are offset relative to the axis of the pinion shaft and when lifted open passages through which the bevel gear may pass. After the capsules have cleared their openings the assembly is first shifted laterally to align the bevel gear with the lower opening, is then lifted again to move the bevel gear through the lower opening, then laterally so that the bevel gear clears the bull gear, then vertically to lift the bevel gear above the bull gear, then laterally to align the bevel gear with the upper opening, then vertically to pass the bevel gear through the upper opening and thereby free the assembly from the housing. This arrangement permits handling of only one pinion shaft assembly including the pinion shaft and its connected gearing, bearings and capsules rather than the whole assembly including both pinion shaft assemblies and their respective bull gear upper housing, etc.
It will be apparent that with the later structure a significant height must be available above the drive to accommodate the length of the pinion shaft above the top of the housing. It sometimes requires the addition of several feet to the height of the building which obviously would be a very costly addition to the capital cost of the mill.
Furthermore, the size of the bottom and top capsule and the requirement to shift the unit laterally, i.e. in a horizontal direction, to clear the bull gear within the housing, extends the dimensions of the housing and increases the clearance normally required between the rougher rolls and edger rolls.